A conventional thermal fixing device for an electro-photographic type image forming device includes a tubular fusing film, a heater disposed in an internal space of the fusing film, a pressure roller, and a nip plate defining a nip region relative to the pressure roller through the fusing film. Further, the fixing device includes a temperature detection element for detecting a temperature of the fusing film. The temperature detection element is disposed at a recessed portion formed in the nip plate and positioned upstream of the nip region. In this fixing device, detection of the temperature of the fusing film enables a temperature of the nip region to be maintained at a predetermined fixing temperature.